Mesmers are often called the most difficult profession to play in Guild Wars, but if played well, can cause a lot of trouble for the enemy. They are best described as the debilitating or the saboteur profession that eschew outright attacks; they instead use misdirection against the foolish and rely on control-based abilities to sap foes of their strength. They can be used to their highest potential when played in a group.

Knowing your enemy as well as yourself is the path to victory for Mesmers, whose primary function is to control the enemy's agenda. Mesmers enjoy a vast array of tools to disrupt or turn enemy actions against them, as well as more standard degenerative and nerfing skills.
Mesmers can push out enormous armor ignoring damage and influence the outcome of the battle with a single well-placed spell. A Mesmer can shut down enemies by interrupting their actions, disabling their skills and removing their adrenaline and energy. They can also cause health degeneration and afflict hexes that reverse the advantages of foes into liabilities, and apply a wide range of conditions. A Mesmer can even use someone's own energy against them (with skills like Energy Burn).

The primary Mesmer attribute, Fast Casting has the inherent effect of reducing the casting time of all mesmer spells, signets and non-mesmer spells with a cast time of 2 seconds or more. In PvE, Fast Casting also causes mesmer skills to recharge 3% faster than normal. Skills in Fast Casting often allow a Mesmer to cast spells more often, such as Mantra of Recovery, or provide skills designed for optimal usage with a Mesmer primary, such as Psychic Instability and Power Return.

Energy denial is a tactic that attacks caster energy instead of health. This is very effective in PvP (where casters have strict energy budgets) and often useless in PvE (where enemies die too fast for energy denial to be effective).

Prioritize targets based on the current state of the battle. Early on, ease pressure on your team by draining the team's offensive casters and countermeasures (e.g. Elementalists). Pressure opponents by draining their defensive measures (Monks and other healers).

Save interrupts to prevent enemies from managing their own energy.

Space out the denial skills, especially as casting slows. In PvP, the average player regains 5 energy approximately every 4 seconds.

Important skills include Energy Burn and Energy Surge and interrupts that disrupt energy management, e.g. Power Leak is a popular choice, as is Shame. Chaos Storm is useful to force casters to move (and therefore interrupt themselves) while denying energy to those who remain.

Skill denial is a technique that renders skills unusable or disrupted; and punishes foes who uses them.

Interrupt selectively: anyone can learn to interrupt any spell; great mesmers interrupt the important ones.

Slowed casting: Use the right skill for the right opponent, e.g. Arcane Conundrum or Migraine would shut down healers but have little effect on melee foes.

Interrupt groups:Panic causes foes to interrupt each other (use on a skill-spammer in the middle of a group for maximum impact). Keystone Signet causes offensive signets to interrupt and damage foes adjacent to their target. Clumsiness causes attacks to interrupt surrounding foes. Cry of Frustration is an effective, but manual AoE interrupt.

Slow down recharge:Complicate and Diversion slows down recharge for a single skill while Blackout and Power Block affect multiple skills on a single opponent's bar. Be careful not to spam either, and remember that the skills might be more effective if used on two different foes.

Punishing hexes:Empathy and Backfire cause attacks and spells (respectively) to damage the caster, in effect causing the foe to shut itself down (rather than commit suicide). Mistrust and Overload punish the allies of foes who take action. Wastrel's Demise and Worry punish foes who are waiting for hexes to expire. (Both are especially effective against pets and minions, since they do not use any skills.) Wastrel's Worry can also be used to predict skill activation and see what they have for those who try to escape it's damage by using skills. Frustration does damage and also rewards the mesmer for each successful interrupted skill.

Threat denial use skills to interrupt, snare, pressure and otherwise neutralize close-combat opponents. It is not as popular in PvP because other professions provide more versatile variations.

Wandering Eye and Clumsiness provide relatively quick recharging interrupts that also disrupt or damage neighboring foes, putting putting early pressure on healers to restore health to the front line. Wait for frontliners to build up energy (watch for Frenzy); hexing them too early is less effective.

A Mesmer has a flexible position in PvE. They can help keep the Tank alive by weakening the enemy, deal damage as well as any other caster profession while improving the effectiveness of your melee teammates and lessen the risk to the Healer(s). Unfortunately this versatility that far exceeds any other profession comes at the price that others will not inherently know what to expect from you. So not only be prepared to explain the role you wish to fill, but also be ready to adjust your role to do what you can do best to compensate for any weaknesses your party has.

Mesmers are best used by players who are well prepared in advance. Knowing the enemy ensures the Mesmer is as effective as possible, for example, if a Mesmer takes a skill bar set for interrupting spell casters, but the area is full of melee based enemies, the Mesmer's bar is wasted. Playing a good Mesmer requires flexibility, advanced forethought and having a strong knowledge of most skills and enemy types in game.

Due to your Fast Casting ability, many Mesmer skills can determine the outcome of a battle before many members of your team have even started their attacks. Many Mesmers are tempted to focus on Domination which has some quite powerful damage skills, i.e. Energy Surge and Chaos Storm; however, these are often most effectively alternated with skills which weaken your enemy. Alternately, especially in the fast paced mission environment, Mesmers often focus on causing fast damage to their enemies by combining their fast cast and shortened recharge time from Fast Casting with damage causing skills like Mistrust.

A powerful although less noticeable style of play is the interruption Mesmer, using skills to stop the enemy from using their spells. These Mesmers usually concentrate on the enemy casters, interrupting healing spells or skills that could hurt the team. This approach is especially beneficial against enemy bosses and thus many Mesmers will carry an interrupt skill even if shutdown is not their focus.

Mesmers can also run a conditional build if they wish with by stacking skills such as Visions of Regret with Empathy and Backfire. These skills can cause major damage to any kind of enemy and are an effective way to deal with melee and Monk bosses, due to the regularity of their actions (the AI will not cast if Backfire or VoR alone will kill itself - giving your party a window of opportunity to kill the foe without retaliation). Using VoR with Wastrel's Worry ensures that the target will take damage no matter what, albeit at the cost of lowering the damage per cast under effects of Visions of Regret. These builds are even more effective in hard mode due to the faster speed at which enemies attack and cast spells.

PvP is the area where Mesmers show their full potential, shutting down the enemy backline single-handedly, assisting spikes with the other hand by removing defensive enchantments with skills like Shatter Enchantment.

The first thing a Mesmer should learn is to think like the enemy. Try to get a feeling for the enemy, when does he cast his spells, how much energy does he have and so on. A well timed Diversion disabling a Word of Healing might cause the enemy to retreat, panic, or die. Most people in PvP are intelligent enough to not use any skill until Diversion ends; they escape from the effects of this skill but they don't heal or inflict damage for six seconds. Knowing the recharge times on spells can greatly help you time your skills, as you won't waste a shutdown when the skill is not yet recharged.

The second thing a Mesmer should learn is to find out what might annoy your team most, like "Do they have a Blinding SurgeElementalist preventing our frontline from killing them?", "Is their Mesmer good enough to prevent our Monks from healing us?" or "We play a condition build, do they have a monk with Restore Condition?". Make sure that your team is communicating to you what they need shut down. A group that's communicating well with their Mesmer will utilize their Mesmer much better. This includes things such as knowing when you have disabled a key skill (like Spirit Bond or Infuse Health) so that your team can act upon that.

While most skills are used in an obvious way, Mesmer skills have very subtle uses that the skill doesn't specify. For instance, using Blackout on a warrior drains all his adrenaline, and using Psychic Distraction goes through anti-interruption skills. You should learn these, and put them to good use, using your bar to the fullest to aid your team. Ether Feast is not commonly on a mesmer bar, but if it is, remember you drain energy, and use that to its full advantage.

Most Mesmer bars in PvP will contain at least one interrupt. Cry of Frustration and Power Drain are two very common examples. On a Mesmer, it's important to note that even your 1/4 second interrupt skills cast faster due to Fast Casting, so you can easily interrupt 1 second spells, which some rangers have difficulty doing. If you still have problems interrupting spells that have short time casting, skills like Arcane Conundrum and Frustration give you extra time to interrupt. Since your skills have slower recharge then most ranger or warrior interrupts, you should be careful to use them only to interrupt key skills where their effect is most used. It's pointless to interrupt low recharge spells in general with Power Drain unless you need the energy, because it will recharge quickly anyway, unless you are using an interrupt spell with a disabling quality, such as Power Block or Power Lock. Knowing which key skills to interrupt defines the Mesmer's role; Restore Conditions, Word of Healing, Guardian and even an enemy Mesmer's Diversion are key skills to keep a mindful eye on.

Lastly, keep in mind that while some hexes last only 6 seconds, a lot can happen in 6 seconds if they are timed properly. Diversion for example, can be placed on a monk when someone is being spiked, and forces that monk to choose to either divert a skill or let the person die. Its not always possible to shut down all the monks, but if you do it successfully, you have a virtually guaranteed kill. By contrast, using the skill randomly allows the monk to just wait for it to wear off with no consequence, since nobody is in danger of death.

Learn to use your bar correctly and efficiently, and you will soon be a force to be reckoned with in PvP.

Because of the low Armor rating of Mesmers, it is best to stay in the midline. Kiting is also an effective tactic. Equip a shield for added armor, and don't overextend.
Also the mesmer stances (Mantra of 'element', physical/elemental resistance) can help greatly in reducing the damage done to the mesmer, often up to 50%.

As a midliner, mesmers have to stay close to the action without placing themselves too close to the enemy team's physical damage. Mesmers are often used to shut down other midliners, and sometimes backliners. Mesmers can choose to focus on shutting down key offense on the other team, which in turn can lower the amount of damage their party members may take.

In PvP, a mesmer's main goal is to not only shut down key members of the opposing team, but also to communicate when he or she does so. If you can tell when an enemy monk is out of energy or if he can't use a particular skill, it would greatly increase the chance of your team getting some kills. If a particular skill was giving a teammate grief (blinds can often do this), diverting it will enable the rest of your team to perform better. Mesmers in pvp are not built for direct damage; they are built for overall team support.

Damage: A Mesmer, like all caster professions, should avoid any direct contact with the enemy. A combination of a maximum of 60 Armor and weak self-defense makes it easy to get killed by even a single enemy. Kiting, proper positioning in the mid or backline are crucial to the Mesmer's survival.

Mesmers rely heavily on spells, which is what they excel at countering. Don't try to cast long activation spells like Diversion if you know another Mesmer (or a Ranger) is watching you to interrupt it.

There are 3 primary ways that the mesmer controls and contains the enemy: shutting down specific opponents, turning the enemy's strengths against itself, or nerfing the enemy's effectiveness. Shutdowns are tools that the mesmer uses to prevent the enemy from acting at all, including interruptions and disruptions. The mesmer can turn the enemy against itself by causing foes to interrupt/disrupt each other or by damaging themselves by attacking, casting, or using skills. Finally, mesmers can snare opponents and force massive armor-ignore degeneration upon them.

Mesmers have skills that can interrupt a target foe's actions, thereby preventing them from doing damage, healing themselves, animating minions, creating spirits, entering a form, etc. These interrupts can also steal energy, cause damage or disable skills. Most interruption skills only interrupt spells and chants, but some can interrupt any skill, like Psychic Distraction. Other interruption skills include: Cry of Frustration, Power Spike, Power Block, Power Drain, Panic and Signet of Distraction. Combined with points in the Mesmer's primary attribute, Fast Casting, these already quick-activating skills are even faster to cast.

Domination skills put Mesmers in command of a foe's health and energy. They can force their foes to choose whether they should cast a spell or attack, when the consequence is loss of health or having their skills disabled (from skills such as Backfire, Empathy or Diversion).

Shut down also comes in the form of disabling spells or spells of an attribute from being used: spells such as Power Lock will disable the interrupted spell for a set amount of time, or the elite Power Block will disable all skills of the same attribute on the enemy's skill bar, effectively knocking them out of play for the duration. Blackout will disable the entire bar of an enemy, but will also disable the Mesmer's as well, so use caution with this skill. While combined with Echo, this skill can shut down the enemy's bar for an entire thirty seconds.

Spells such as Simple Thievery and Arcane Thievery are a unique form of shut down that essentially remove skills from other player's bars and place them on the Mesmer's for a varying period of time, sometimes allowing the Mesmer to use these stolen skills to their advantage if they steal another Mesmer's skills, or skills of an attribute they are also using on their bar. In the case of Simple Thievery the Mesmer can steal a Resurrection Signet if they interrupt it, giving their team/party an advantage of an extra res if all sigs have been used or no other res skills are available.

Mesmers can be very effective at reducing the effectiveness of spell casters. Hexes like Frustration or Migraine make the foe cast spells slower, enabling easier interrupts and reduced spamming of spells. Frustration has the added benefit of dealing damage every time the caster is interrupted. Some of the skills that cause the foe to cast spells slower are: Migraine, Arcane Conundrum, Frustration, and Stolen Speed.

Mesmers can be effective damage dealers in PvE. Illusion Magic includes Clumsiness and Wandering Eye recharge quickly and deal considerable damage to multiple targets. Domination Magic includes the elite Panic hex, as well as potent damage dealing hexes such as Mistrust and Wastrel's Demise. The Sunspear skill Cry of Pain skill is useful for AoE damage.

Mesmers can call on Inspiration Magic skills (like Energy Drain) to steal energy directly from their enemies. By taking the energy of their foes, the Mesmers can reduce the foe's effectiveness, as well as provide extra energy for themselves for casting more offensive spells at their foes. Stealing Energy from a Monk, for example, may severely hinder his ability to heal his allies. Some common skills used for energy denial are: Energy Surge, Energy Burn, Shame, Guilt, and Energy Drain.

The Mesmers that specialize in health degeneration mainly use Illusion Magic hexes like Conjure Nightmare, Conjure Phantasm, Images of Remorse, Shrinking Armor, Illusion of Pain, Migraine, etc. Keep in mind, though, that health degeneration greater than -10 will only cap at -10. However, the degeneration over -10 can still offset added health regeneration. E.g. an enemy has degeneration worth -15 which is limited to -10. The enemy then casts a +6 regeneration Healing Breeze. Instead of having -4 degeneration, the hidden degeneration reduces the regeneration, leaving the enemy at -9 degeneration. Mesmers using health degeneration hexes can use Mantra of Persistence to make Illusion Magic hexes last longer.